1. Field of the Invention
The present invention relates to an automotive vehicle brake assembly, and more particularly to a so-called grade-holding brake system for keeping a vehicle stopped after the vehicle has halted.
2. Description of the Related Art
Recently, grade-holding brake system assemblies for automotive vehicles have been developed that automatically apply the brakes to make it possible to easily start off in a vehicle, such as an automobile on a slope without abrupt pedal changes from the brake pedal to the accelerator pedal, or that dispense with the need to continuously step on the brake pedal while waiting for a traffic signal to change or during traffic jams to thereby moderate fatigue caused by the brake operation.
Conventionally, such a type of a grade-holding brake system is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-48222. In this conventional assembly, when the vehicle is halted and the parking brake is applied, the braking force is increased to automatically apply the brakes to reduce the fatigue caused by the driver's brake operation and also to positively maintain the halted condition of the vehicle.
However, when moving in a traffic jam and utilizing the grade-holding function of the above-described conventional assembly, it is necessary to operate the parking brake each time the vehicle comes to a halt. Also, in many vehicles, the parking brake is manually operated. Such manual operation is liable to be troublesome for the driver and make him feel fatigue. Accordingly, there is a problem in that the driver may feel that the operation of the parking brake is troublesome, and ultimately feel fatigued.
Further, the above-described problem occurs not only when moving in traffic jams but also when starting the vehicle off on a slope.
Accordingly, in order to eliminate or alleviate the above-described problems, it is an object of the present invention to provide a grade-holding brake system which makes it possible to readily start off a vehicle on a slope without the necessity of abrupt pedal changes from a brake pedal to an accelerator pedal, which dispenses with the need to continuously step on the brake pedal when waiting for a traffic signal to change or during traffic jams to thereby moderate the fatigue caused by the brake operation, and without making a driver feel that the operation is troublesome.
According to one aspect of the present invention, there is provided a grade-holding brake system for a vehicle comprising: a master cylinder connected to a booster device for amplifying a brake force applied by a driver to a brake pedal; a wheel cylinder for converting a pressure fed from said master cylinder into a braking force for a wheel; a brake switch for detecting an amount of depression of the brake pedal; an accelerator switch for detecting an amount of an accelerator pedal depression; a vehicle speed sensor for detecting a speed of a vehicle on which the brake system is mounted; a pressure controlling means for controlling the pressure within said wheel cylinder independently of the operation of the brake pedal; and a controller for controlling actuation of said pressure controlling means for controlling the pressure within said wheel cylinder. The controller, for controlling the pressure within said wheel cylinder, performs: a brake pedal depression detecting step for detecting whether the brake pedal is being depressed or not on the basis of a detection signal of said brake switch; an accelerator pedal depression detecting step for detecting whether said accelerator pedal is being depressed on the basis of a detection signal of said accelerator switch; a vehicle halted determination step for determining a vehicle halt state of the vehicle on the basis of a detection signal of said vehicle speed sensor; a holding condition establishment step for establishing a brake holding condition for holding a braked condition of a brake at least when the brake pedal is depressed and when the vehicle is in the vehicle halted condition; a holding condition release step for establishing a brake release condition for releasing the braked condition of the brake at least when the accelerator pedal is depressed; a first holding command step for sending a pressure holding command to said pressure controlling means and maintaining the pressure within said wheel cylinder until the brake release condition is established when the brake holding condition is established and when the brake release condition is not established; and a pressure decrease command step for sending a pressure to thereby decrease the pressure within said wheel cylinder decrease command to said pressure controlling means and releasing the brake when the brake release condition is established.
In a preferred form of the invention, the system, further comprising: a wheel cylinder pressure detector for detecting the pressure within said wheel cylinder and a pressure increase means controlled by said controller for increasing the pressure within said wheel cylinder independently of the operation of the brake pedal. The controller, for controlling the pressure within said wheel cylinder, further performs: a target pressure setting step for setting a target pressure needed within said wheel cylinder to obtain a target braking force; a comparative determination step for comparatively determining a detected pressure of said wheel cylinder pressure detector with the target pressure; and a second holding command step for, when the brake holding operation by said pressure controlling means is established and when the brake release condition is not established, performing said first holding command step when the detected pressure is higher than the target pressure and for increasing the pressure within said wheel cylinder up to the target pressure by said pressure increasing means, and at the same time, maintaining the pressure within said wheel cylinder until the brake release condition is established.
In a further preferred form of the invention, the system, further comprising: a braking force detecting means for detecting the braking force, wherein the brake holding condition is established at least when the brake pedal is depressed, and when the vehicle is at a standstill, and when a braking force equal to or greater than a predetermined value continues for a predetermined period of time.
In a still further preferred form of the invention, the brake holding condition is established at least when the brake pedal is depressed, and when the edition that the vehicle is stopped is continued for a predetermined period of time.
In accordance with a still further aspect of the invention, said second holding command step comprises a step for maintaining or increasing the pressure within said wheel cylinder by virtue of said pressure increasing means to thereby maintaining the pressure within said wheel cylinder at the target pressure when the brake pedal is first released after the brake holding condition has been established.
In accordance with a yet further aspect of the invention, said target pressure setting step comprises a step for setting the pressure within said wheel cylinder as the target pressure when the brake holding condition is established.
In a further preferred form of the invention, said target pressure setting step comprises a step for setting a pressure as the target pressure based upon the pressure within said wheel cylinder when the brake holding condition is established.
In a further preferred form of the invention, said target pressure setting step comprises a step for setting the target pressure obtained by adding a predetermined value to the pressure within said wheel cylinder when the brake holding condition is established.
In a further preferred form of the invention, the system, further comprising: a selection switch for allowing a driver to select operation/non-operation of said grade-holding brake system, wherein the brake release condition is established even if the selection switch is in a non-operating condition.
In a further preferred form of the invention, said controller further performs a shift range detecting step for detecting a shift range selected by a driver in a vehicle provided with an automatic transmission, wherein the brake release condition may also be established when the shift range is in park.
In a further preferred form of the invention, said controller further performs a brake re-depress detecting step for detecting that the brake pedal has been depressed again when the first and/or second holding command step(s) are/is executed and the brake pedal is released, and the brake release condition is established even when the brake pedal is depressed again.
In a further preferred form of the invention, said pressure controlling means comprises a first cut-off valve disposed in a first brake tubing for connecting the master cylinder and the wheel cylinder to each other for opening/closing said first cut-off valve to hold or decrease the pressure within said wheel cylinder.
In a further preferred form of the invention, said pressure increase means comprises a pressure booster means disposed in parallel with said first brake tubing in a brake tubing for connecting said master cylinder and said wheel cylinder to each other, and a second cut-off valve disposed at least closer to said master cylinder at least than said Pressure booster means, wherein the pressure within said wheel cylinder is increased or held by using said pressure booster means and said second cut-off valve to thereby control the braking force.
In a further preferred form of the invention, one of said brake depressing amount detecting step and said brake re-depress detecting step is performed by a brake switch for outputting that the brake pedal is depressed to a predetermined depth.
In a further preferred form of the invention, one of said brake depressing amount detecting step and said brake re-depress detecting step is performed by a master cylinder pressure detector for detecting a pressure at a location closer to the master cylinder than said first cut-off valve.
In a further preferred form of the invention, said brake depressing amount detecting step is performed by a wheel cylinder pressure detector for detecting a pressure closer to the wheel cylinder than said first cut-off valve.
In a further preferred form of the invention, the system, further comprising an alarm for informing the driver of the operation/non-operation of said grade-holding brake system, wherein said controller further performs at least one of a holding alarm step for sounding said alarm when the brake holding condition is established and when the brake release condition is not established, and a release alarm step for sounding said alarm when the brake release condition is established.
In a further preferred form of the invention, the alarm sound of the holding alarm step is different from the alarm sound of the release alarm step.
In a further preferred form of the invention, the system, further comprising a lamp for informing the driver of the operation/non-operation of said grade-holding brake system, wherein said controller further performs a lighting step for lighting said lamp until the brake release condition is established when the brake holding condition is established and when the brake release condition is not established, and a turn-off step for turning said lamp off when the brake release condition is established.
In a further preferred form of the invention, the system, further comprising an announcing device for notifying the driver of the operation/non-operation of said grade-holding brake system to the driver, wherein said controller further performs one of an operation announcing step for announcing a message indicating the operation of said grade-holding brake system when the brake holding condition is established and when the brake release condition is not established, and a non-operation announcing step for announcing a message the non-operation of said grade-holding brake system when the brake release condition is established.